Java - 如何逐字节读取 .dat 文件

Question

我正在尝试使用 Java 读取 .dat，而不使用其他类。 这是文件的结构: header 连载:字；//2字节 文件名:字符串[255]；//1字节 日期:字；//2字节 字段编号:Word；//2字节 记录数:Word；//2字节

Info about Fields 
    FieldCode: Word;   //2 bytes
    FieldName: ShortString;   //1 byte

Info in Field 
    FieldCode: Word;  //2 bytes
    FieldText: String[255];  //1 byte

    DateTime = double

我必须知道的是如何使用 BufferedReader 获取每个字节，将其读取为 int，然后将相同的 int 转换为字符串并将其显示在屏幕上。 我可以创建不同的方法来读取每种类型的数据吗？我可以让它同时读取2个字节吗？

更新:

    package binarios5;

import java.io.FileNotFoundException;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;

public class Main5 
{

    public static void main(String[] args) throws FileNotFoundException, IOException 
    {

        try 
        {
            Path path = Paths.get("C:\\\\Dev-Pas\\\\EXAMEN2.dat");
            System.out.println("File open");
            byte[] bytes = Files.readAllBytes(path);
            ByteBuffer buffer = ByteBuffer.wrap(bytes);
            buffer.order(ByteOrder.BIG_ENDIAN);
            short serial = buffer.getShort();
            System.out.println("----[CONTENIDO DEL ARCHIVO]--------------------");
            System.out.println("Nro. de Serie: " + serial);
            int largoCadena = buffer.get();//Bytes 1 int Longitud de la cadena
            //System.out.println("largoCadena: " + largoCadena);//33
            byte[] bytesChar = new byte[largoCadena];//CString
            buffer.get(bytesChar);
            String nombre = new String(bytesChar, StandardCharsets.ISO_8859_1);
            System.out.println("Nombre: " + nombre);

            short date = buffer.getShort();//FALTA DECODIFICAR FECHA
            System.out.println("Fecha sin procesar. "+date);//FALTA DECODIFICAR FECHA

            short cantCampos = buffer.getShort(); //cantidad de campos que tienen los registros
            System.out.println("Cantidad de Campos Customizados: "+cantCampos);//debe decir 4
            int[] codCampo = new int[cantCampos];
            String[] nombreCampo = new String[10];


            for (int i = 0; i < cantCampos; i++) //leer RegType segun la cantidad de campos
            {
                codCampo[i] = buffer.getShort();//Bytes 2 codigo del campo
                int largoCadena2 = buffer.get();//Bytes 1 int Longitud de la cadena
                byte[] bytesChar2 = new byte[largoCadena2];
                buffer.get(bytesChar2);
                nombreCampo[i] = new String(bytesChar2, StandardCharsets.ISO_8859_1);
            }

            for (int i = 0; i < cantCampos; i++)//mostrar codigos y campos
            {
                System.out.println("Campo [codigo: " + codCampo[i] + ", descripcion: " + nombreCampo[i] + "]");
            }

            short cantRegistros = buffer.getShort();//cantidad de registros total
            System.out.println("Cantidad de Registros: "+cantRegistros);
            System.out.println("-----------------------");//OK

            String[] contenidoCampo = new String[10];
            for (int i = 0; i < cantRegistros; i++) //leyendo RegData 5 veces
            {
                short cantCamposCompletos = buffer.getShort();

                for (int j = 0; j < cantCamposCompletos; j++)
                {
                    short codCampoInterno = buffer.getShort();
                    int largoCadena3 = buffer.get();
                    byte[] bytesChar3 = new byte[largoCadena3];
                    buffer.get(bytesChar3);
                    contenidoCampo[j] = new String(bytesChar3, StandardCharsets.ISO_8859_1);
                    System.out.println(nombreCampo[j]+": "+contenidoCampo[j]); 
                }
                System.out.println("-----------------------");
            }

            System.out.println("----[FIN CONTENIDO DEL ARCHIVO]-----------------");
        } 
        catch (IOException e)
        {
            System.out.println("File I/O error!");
        }

    }


}

Answer 1

在java中，Reader和Writer用于Unicode文本、字符串、2字节字符。

对于二进制数据，byte[]需要一个InputStream、OutputStream。

可以使用输入流:

BufferedInputStream in = new BufferedInputStream(new FileInputStream(...));

就您而言，您想阅读简短的内容等。为此，您可以将其包装在 DataInputStream 周围。

但是，使用 ByteBuffer 是最容易开始的。可以从文件(FileChannel)中读取，但简单的情况是:

Path path = Paths.get("C:/xxx/yyy.dat");
byte[] bytes = Files.readAllBytes(path);
ByteBuffer buffer = ByteBuffer.wrap(bytes);
//buffer.order(ByteOrder.LITTLE_ENDIAN); // So short is read as LSB,MSB

已解决:

// Header
short serial = buffer.getShort();
byte[] fileNameB = new byte[255];
buffer.get(fileNameB);
// If 0 terminated asciz string:
int len = fileNameB.length;
for (int i = 0; i < fileNameB.length; ++i) {
    if (fileNameB[i] == 0) {
        len = i;
        break;
    }
}
String fileName = new String(fileNameB, 0, len, StandardCharsets.ISO_8859_1);

short date = buffer.getShort();
short fieldNumbers = buffer.getShort();
short numbersOfRecords = buffer.getShort();

for (int fieldI = 0; fieldI < fieldNumber; ++fieldI) {
    // Info about Fields 
    short fieldCode = buffer.getShort();
    //byte fieldName: ShortString;   //1 byte
}

字段信息 字段代码:Word；//2字节 字段文本:字符串[255]；//1字节

DateTime = double

<小时/>

String getPascalString(ByteBuffer buffer) {
    int length = buffer.get() & 0xFF;
    byte[] bytes = new byte[length];
    buffer.get(bytes);
    return new String(bytes, StandardCharsets.ISO_8859_1);
}

Will deliver: d:/documentos/te...

short packedDate = buffer.getShort();
int year = packedDate & 0x7F; // + 1900?
int month = (packedDate >> 7) & 0xF:
int day = (packedDate >> 11) & 0x1F;